1. Field of the Invention
The invention relates to substituted 5-(cyclohex-2-en-1-yl)penta-2,4-dienes and 5-(cyclohex-2-en-1-yl)pent-2-en-4-ynes, to processes for their preparation and their use for enhancing stress tolerance in plants to abiotic stress, and/or for increasing plant yield.
2. Description of Related Art
It is known that particular 5-(1,2-epoxy-2,6,6-trimethylcyclohexyl)-3-methylpenta-2,4-dienoic acids and derivatives thereof have properties which influence plant growth (cf. NL6811769). The growth-moderating effect of certain 1,2-epoxy analogs of abscisic acid on rice seedlings is also described in Agr. Biol. Chem. 1969, 33, 1357 and Agr. Biol. Chem. 1970, 34, 1393. The use of substituted 5-cyclohex-2-en-1-ylpenta-2,4-dienyl- and 5-cyclohex-2-en-1-ylpent-2-en-4-ynylols, 5-cyclohex-2-en-1-ylpenta-2,4-dienyl and 5-cyclohex-2-en-1-ylpent-2-en-4-ynyl thioethers and 5-cyclohex-2-en-1-ylpenta-2,4-dienyl- and 5-cyclohex-2-en-1-ylpent-2-en-4-ynylamines as inhibitors of epoxycarotenoid dioxygenase and as germination inhibitors is described in US2010/0160166. The preparation of particular abscisic acid derivatives with a 3-methyl substituent in the 2,4-pentadienoic acid unit and the use thereof for influencing germination and plant growth is described in U.S. Pat. No. 5,518,995 and EP0371882. It is additionally known that particular abscisic acid derivatives with a 3-methyl substituent can be used to increase tolerance of plants to low temperatures (cf. WO94/15467). The increase in the yield of soybean seeds through use of a mixture of abscisic acid and a suitable fertilizer is described in U.S. Pat. No. 4,581,057.
It is likewise known that 5-(cyclohex-2-en-1-yl)-3-methylpenta-2,4-dienoic acid derivatives having unsaturated substituents at position C6 of the 5-cyclohex-2-en-1-yl unit can influence the water balance and the germination of plants (cf. WO97/23441). Described are furthermore trifluoromethyl, alkyl and methoxymethyl substituents at position C6 of the 5-cyclohex-2-en-1-yl unit in 5-(cyclohex-2-en-1-yl)-3-methylpenta-2,4-dienoic acids (cf. Biosci. Biotech. Biochem. 1994, 58, 707; Biosci. Biotech. Biochem. 1995, 59, 699; Phytochem. 1995, 38, 561; Bioorg. Med. Chem. Lett. 1995, 5, 275). Bicyclic tetralone-based 3-methylpenta-2,4-dienoic acid derivatives are described in WO2005108345.
It is also known that abscisic acid and derivatives thereof can be used as pharmaceutically active compounds for regulation of calcium transport (cf. EP240257).
The preparation of an abscisic acid derivative having a 3-hydroxymethyl side chain, (2E,4E)-3-(hydroxymethyl)-5-(1-hydroxy-2,6,6-trimethyl-4-oxocyclohex-2-en-1-yl)penta-2,4-dienoic acid, is described in Org. Biomol. Chem. 2006, 4, 4186.
It is known that plants can react with specific or unspecific defense mechanisms to natural stress conditions, for example cold, heat, drought stress (stress caused by aridity and/or lack of water), injury, pathogenic attack (viruses, bacteria, fungi, insects) etc., but also to herbicides [Pflanzenbiochemie [Plant Biochemistry], p. 393-462, Spektrum Akademischer Verlag, Heidelberg, Berlin, Oxford, Hans W. Heldt, 1996; Biochemistry and Molecular Biology of Plants, S. 1102-1203, American Society of Plant Physiologists, Rockville, Md., eds. Buchanan, Gruissem, Jones, 2000].
In plants, there is knowledge of numerous proteins, and the genes which code for them, which are involved in defense reactions to abiotic stress (for example cold, heat, drought stress, salt, flooding). Some of these form part of signal transduction chains (for example transcription factors, kinases, phosphatases) or cause a physiological response of the plant cell (for example ion transport, deactivation of reactive oxygen species). The signaling chain genes of the abiotic stress reaction include inter alia transcription factors of the DREB and CBF classes (Jaglo-Ottosen et al., 1998, Science 280: 104-106). The reaction to salinity stress involves phosphatases of the ATPK and MP2C types. In addition, in the event of salinity stress, the biosynthesis of osmolytes such as proline or sucrose is often activated. This involves, for example, sucrose synthase and proline transporters (Hasegawa et al., 2000, Annu Rev Plant Physiol Plant Mol Biol 51: 463-499). The stress defense of the plants to cold and drought uses some of the same molecular mechanisms. There is a known accumulation of what are called late embryogenesis abundant proteins (LEA proteins), which include the dehydrins as an important class (Ingram and Bartels, 1996, Annu Rev Plant Physiol Plant Mol Biol 47: 277-403, Close, 1997, Physiol Plant 100: 291-296). These are chaperones which stabilize vesicles, proteins and membrane structures in stressed plants (Bray, 1993, Plant Physiol 103: 1035-1040). In addition, there is frequently induction of aldehyde dehydrogenases, which deactivate the reactive oxygen species (ROS) which form in the event of oxidative stress (Kirch et al., 2005, Plant Mol Biol 57: 315-332). Heat shock factors (HSF) and heat shock proteins (HSP) are activated in the event of heat stress and play a similar role here as chaperones to that of dehydrins in the event of cold and drought stress (Yu et al., 2005, Mol Cells 19: 328-333).
A number of signaling substances which are endogenous to plants and are involved in stress tolerance or pathogenic defense are already known. Examples here include salicylic acid, benzoic acid, jasmonic acid or ethylene [Biochemistry and Molecular Biology of Plants, p. 850-929, American Society of Plant Physiologists, Rockville, Md., eds. Buchanan, Gruissem, Jones, 2000]. Some of these substances or the stable synthetic derivatives and derived structures thereof are also effective on external application to plants or in seed dressing, and activate defense reactions which cause elevated stress tolerance or pathogen tolerance of the plant [Sembdner, and Parthier, 1993, Ann. Rev. Plant Physiol. Plant Mol. Biol. 44: 569-589].
It is additionally known that chemical substances can increase the tolerance of plants to abiotic stress. Such substances are applied either by seed dressing, by leaf spraying or by soil treatment. For instance, an increase in abiotic stress tolerance of crop plants by treatment with elicitors of systemic acquired resistance (SAR) or abscisic acid derivatives is described (Schading and Wei, WO200028055, Churchill et al., 1998, Plant Growth Regul 25: 35-45). In addition, effects of growth regulators on the stress tolerance of crop plants have been described (Morrison and Andrews, 1992, J Plant Growth Regul 11: 113-117, RD-259027). In this context, it is likewise known that a growth-regulating naphthylsulfonamide (4-bromo-N-(pyridin-2-ylmethyl)naphthalene-1-sulfonamide) influences the germination of plant seeds in the same way as abscisic acid (Park et al. Science 2009, 324, 1068-1071). It is also known that a further naphthylsulfonamide, N-(6-aminohexyl)-5-chloronaphthalene-1-sulfonamide, influences the calcium level in plants which have been exposed to cold shock (Cholewa et al. Can. J. Botany 1997, 75, 375-382).
Similar effects are also observed on application of fungicides, especially from the group of the strobilurins or of the succinate dehydrogenase inhibitors, and are frequently also accompanied by an increase in yield (Draber et al., DE3534948, Bartlett et al., 2002, Pest Manag Sci 60: 309). It is likewise known that the herbicide glyphosate in low dosage stimulates the growth of some plant species (Cedergreen, Env. Pollution 2008, 156, 1099).
In the event of osmotic stress, a protective effect has been observed as a result of application of osmolytes, for example glycine betaine or the biochemical precursors thereof, e.g. choline derivatives (Chen et al., 2000, Plant Cell Environ 23: 609-618, Bergmann et al., DE4103253). The effect of antioxidants, for example naphthols and xanthines, to increase abiotic stress tolerance in plants has also already been described (Bergmann et al., DD277832, Bergmann et al., DD277835). However, the molecular causes of the antistress action of these substances are substantially unknown.
It is additionally known that the tolerance of plants to abiotic stress can be increased by a modification of the activity of endogenous poly-ADP-ribose polymerases (PARP) or poly-(ADP-ribose) glycohydrolases (PARG) (de Block et al., The Plant Journal, 2004, 41, 95; Levine et al., FEBS Lett. 1998, 440, 1; WO0004173; WO04090140).
It is thus known that plants possess several endogenous reaction mechanisms which can bring about effective defense against a wide variety of different harmful organisms and/or natural abiotic stress.
Since the ecologic and economic demands on modern plant treatment compositions are increasing constantly, for example with respect to toxicity, selectivity, application rate, formation of residues and favorable manufacture, there is a constant need to develop novel plant treatment compositions which have advantages over those known, at least in some areas.